1. Field of the Invention
The present invention relates to a storage system and storage system control method.
2. Description of the Related Art
Storage systems are known in which respective storage devices are installed in a plurality of geographically separated sites, and the respective sites are connected to each other via a communications network (U.S. Pat. No. 5,742,792). In such storage systems, the memory contents of the storage devices installed at the respective sites are matched by a technique called remote copying. Accordingly, even in cases where some site becomes unusable, the business service [of this site] can be continuously provide by utilizing the remaining normal sites.
Remote copying refers to a technique for matching the memory contents(data) of a plurality of physically separated storage devices without interposing a host computer or server as a higher device. In cases where remote copying imaging signal processing circuit performed, a logical volume constituting the copying source is prepared inside the storage device of one site, and a logical volume that constitutes the copying destination is prepared in the storage device of another site. These two logical volumes form a copying pair. In cases where data is updated on the logical volume of the copying source, this updating is reflected in the logical volume of the copying destination.
Furthermore, a cluster system is also known in which a single aggregate is formed by loosely coupling a plurality of servers so as to form a single server in apparent terms, and a service is provided to the client machines.
In cases where data contents are synchronized among a plurality of physically separated sites, and a storage service is provided to respective separate servers at each of the respective sites, the data cannot be synchronized among the respective sites if trouble occurs in remote copying function. Accordingly, differences are generated in the data contents among the respective sites. If a storage service is provided in such a state, there is a possibility that erroneous operation will be performed using old data groups in which updated data is not reflected in the site that has the copying destination logical volume.
It is also conceivable that a cluster system might be used in addition to a remote copying technique in order to improve the resistance to trouble. However, in a cluster system, a shared logical volume is simply used exclusively by a failover source server and a failover destination server. In the case of a cluster system, the shared logical volume is merely recognized as a single volume; no consideration is given to the question of whether or not data is synchronized among different logical volumes installed in separate sites. Accordingly, an effective disaster recovery system cannot be constructed merely by combining a cluster system and a remote copying system.